1. Field of the Invention
This invention relates to prosthetic heart valves and, more particularly, to an apparatus and method for protecting valve cusp material against inadvertent needle puncture or tear during the implantation of the valve in the patient.
2. Description of Prior Art
Prosthetic tissue heart valves constructed of autologous or hemologous fascia lata, dura matter or heterologous pericardium are described in U.S. Pat. Nos. 4,084,268 and 4,172,295. Typically, such valves are constructed by securing the tissue around the outside of a valve stent or framework having a circular base at one end and three axially-extending commissure posts interconnected by valleys at the other end. The tissue is supported at three points by the stent posts while the tissue intermediate the stent posts extends through the valleys and into the center of the stent to form three valve cusps.
The valve stent also includes a sewing cushion around the circular base portion as illustrated in the above-referenced patents. The sewing cushion provides a means for attaching the valve to the patient by suturing through the sewing cushion. In one method of implanting the valve, a plurality of sutures are placed through the sewing cushion and the mounting site in the patient using an interrupted mattress stitch while holding the valve several inches away from the mounting site. When all the sutures are in place, the valve is guided down the suture lines into the mounting position and the sutures are tied off.
In the case of valves constructed of pericardium or other natural tissues, the tissue is positioned outside the stent as illustrated in the above-referenced patents. The tissue is thusly exposed and subject to needle damage as the mounting sutures are placed through the sewing ring. Since the operating area is cramped and vision may be limited, especially in the case of mitral valve replacement where the cusps of the valve are directed away from the surgeon and shielded from view by the sewing ring, great care must be taken when passing the mounting sutures through the sewing ring to avoid accidentally piercing or tearing the valve tissue. Because of the delicate nature of the tissue, a single needle hole can seriously compromise the long-term performance and durability of the valve.
It is accordingly an object of the present invention to provide a method and device for protecting the cusp material of a prosthetic heart valve against needle damage during the installation procedure. It is a further object of the present invention to provide a protective device which is easily removed from the heart valve after all the mounting sutures are in place. These and other objects of the present invention will be apparent from the ensuing description and claims.